The present invention relates to a gear pump and a fuel transfer system using the gear pump, especially to a gear pump which is effective for use in a fuel system of a vehicle engine.
A gear pump used for an internal combustion engine and an automatic transmission gear, and a fuel transfer apparatus including a gear pump, are disclosed in JP-A-271577/1991 and JP-A-294578/1990, respectively.
Further, JP-A-231688/1992 discloses a gerotor pump comprising inner and outer gear rotors for forming a pump space between teeth engaging with each other, the volume of which changes with the expanding and narrowing in a circumferential part, a fluid inlet and a fluid outlet, which are isolated from each other, communicating with the pump space and opening in their axial directions; an apparatus connected to the inner gear rotor, for driving the inner gear rotor so as to transfer fluid from the inlet to the outlet; an apparatus including a housing containing the inner and outer gear rotors, for guiding rotation of the inner gear rotor; and a bearing apparatus provided adjacent to the outlet of the housing, for bearing the outer gear rotor, wherein the outer gear rotor can freely move besides being born by the bearing apparatus, and a fluid leaking gap in an expanded pump space is reduced by the outer gear rotor, which is pressed to the bearing apparatus by the pressure of fluid in a narrowed pump space.
Further, Japanese Patent Publication 16300/1970 discloses an oil pressure gear pump or motor in which a sealing member for sealing tooth parts of teeth engaging with each other in a sealed-up gear case is provided at a part neighboring a gear working place at a low pressure side of the pump, set separately from the gear case, and oil passing holes are formed in the sealing member.
By separating the fuel pump from the engine, the possibility of increasing the amount of fuel to be injected at the time of engine starting is improved, and any restriction on the location of the pump is removed, which improves the freedom of design, and so a motor driven gear pump provided in a vehicle separately from the engine has been devised. However, it has been required that the operational efficiency or the reduction in fuel consumption of a conventional gear pump is to be improved.
The gear pump disclosed in Japanese Patent Publication 16300/1970 has a feature that its structure is simple, and it has a high efficiency and good reliability when using a fluid of high viscosity. However, as mentioned in the publication, since the disclosed gear pump is used as an oil pressure gear pump, the pump is not suitable for use as a fuel pump for a vehicle in which a low viscosity fuel is used. In a fuel pump of a vehicle, used mainly for transferring gasoline, the occurrence of cavitation should be prevented. Moreover, since a fuel pump is used in a fuel system of a vehicle, the pump is required to have an excellent pressure rising performance and to make it possible to attain a low fuel consumption.